a viewer on a CD will be started at a lot differnt PC's.
If the viewer starts at the first time on a PC, the program shows a message, that it is not the default viewer for DICOM files at the system and the user can answer, if it wants to change its own windows setting.

Normaly I answer with no, because I don't want to change my windows setting.
If I answer with yes, then the system links the files with the dcm extension to the program at the CD.
But the CD would be removed and the call ends with an error message. One mistake (press yes) and the (simple) user can no more view at its own dcm files by double click